In order to control production of plastics, textiles, fibers and adhesive materials, industries involved in their production have quality standards for initial chemical reactants, chemical intermediates and related by-products. These industries are also concerned with streamlining any purification processes and minimizing the amount of by-products and impurities that need to be collected, treated and either recycled or disposed of by the manufacturer. Minimizing the by-products and impurities in the chemical reactants and intermediates can also decrease the number of purification steps and ultimately decrease the cost of production of the final product.
U.S. Pat. No. 3,850,910 (issued to Goettsch on Nov. 26, 1974) shows a typical/conventional process for the production and recovery of pure ε-caprolactam. In Goettsch, the crude caprolactam product is purified through a series of cation and anion exchangers that remove impurities. However, the Goettsch process results in caprolactam yields that may be considered suitable for conventional processes, but are not considered suitable yields when trying to improve the commercial viability of a process or method of producing and/or purifying ε-caprolactam.
U.S. patent application Ser. No. 2002/0040137 A1 by Holerich et al. and “Beckmann Rearrangement of Cyclohexanone Oxime over Borate-Pillared LDHs” from J. Chin. Chem. Soc., Vol. 46, No. 5, 1999 describe processes that attempt to purify crude caprolactam. However, these processes utilize technologies that may not translate well into a commercial purification process, such as fluidized beds and borate-pillared LDHs, or may be considered too costly and/or bulky to use or incorporate into a commercial production/purification process.
U.S. Pat. No. 4,017,482 (issued to Gath on Apr. 12, 1977) describes a process of combining crude caprolactam obtained from a Beckmann rearrangement of cyclohexanone oxime in oleum with the gas-phase rearrangement of cyclohexanone oxime in the presence of catalysts. This process of simultaneously purifying two different sources of crude caprolactam requires several additional and possibly unnecessary processing steps that would hinder an efficient commercial amide production method and/or process. Moreover, this process is not practiced commercially.
U.S. Pat. No. 4,804,754 (issued to DeDecker et al. on Feb. 14, 1989) discloses a process of purifying a single stream of crude caprolactam by after treating the reaction mixture in a relatively low temperature delay zone, which can be an elongated structure or large tube, for a specified time period of 10 to 600 minutes. However, the temperature contemplated by DeDecker does not exceed the maximum temperatures specified for a successful Beckmann rearrangement, which can lead to lengthy processing times and delay times while the crude caprolactam is in the aftertreatment stage.
Based on industry standards, cost concerns, environmental concerns and quality assurance standards, methods should be utilized that a) remove or reduce the amount of significant or influential impurities in the chemical reactant or intermediate; b) facilitate removal or reduction of significant or influential impurities in the chemical reactant or intermediate; and c) streamline the process of further production incorporating the chemical reactant or intermediate.
As described herein, in order to produce at least one of the amide compounds described herein, including lactams and ε-caprolactam, a method of production has been developed that not only produces at least one amide compound, but also reduces or substantially eliminates certain impurities and thus improves the quality of the amide compound and can improve any of the products produced using the amide compound. The method of producing at least one amide comprises: a) providing an organic liquid comprising at least one oxime (subsequently referred to as liquid oxime); b) providing at least one catalyst; c) adding the at least one catalyst to the liquid to form a rearrangement mass, wherein the rearrangement mass comprises at least one amide, at least one impurity, and the at least one catalyst; and d) heating the rearrangement mass in order to sulfonate, break down and/or significantly reduce at least some of the at least one impurity in the rearrangement mass.
Upon and after heating, the rearrangement mass will comprise at least one amide, at least one catalyst and at least one broken down or sulfonated impurity and/or an impurity that has been reduced in concentration. At this point, the at least one amide should be removed from the remaining constituents of the post-heating step rearrangement mass by using a purification method. A contemplated method of purifying the at least one amide comprises: a) adding water, a base and solvent to the rearrangement mass to form a neutralized solution; b) separating the neutralized solution into an aqueous phase and an organic phase; c) distilling the organic phase to produce a solvent distillate and an impure amide; d) performing a crystallization purification step on the impure amide; and e) distilling and drying the crystallization amide product to produce a final purified amide product.